I am new to this site and came across your post. Did you end up installing this? I'm curious as to your experience.
Their themes look interesting to me, though I have some concerns as well. A fair number of the sites on their showcase page are no longer in business, which isn't a great sign. And people are saying some bad things about them on this site here. However, I haven't completed my research and they do have some interesting features for a reasonable price. They have 24/7 online chat for sales and support which is impressive. So that's another place you could ask your question.
I asked their support about this question, because I was looking to do the same thing you were. They are not plug-ins...they are themes. They can be installed on separate sub-pages of a site. They also mentioned WordPress MU, but stated that they don't have experience with it. I don't either so I don't know if that would be a solution.